The present invention relates to a dielectric ceramics having a high dielectric constant xcex5 r and a high Q value of resonance acutance in a high frequency region such as of microwave and millimeter-wave, as well as a dielectric resonator. More particularly, the invention relates to a dielectric ceramics used for a variety of resonator materials, MIC (Monolithic IC) dielectric substrate materials, dielectric waveguide materials, multilayer ceramic capacitors and the like which are used, for example, in the mentioned high frequency region, as well as a dielectric resonator.
Dielectric ceramics have been widely used for dielectric resonators, MIC dielectric substrates and waveguides in a high frequency region such as of microwave and millimeter-wave. The dielectric ceramics are generally required to have the following three principal properties:
1) A high dielectric constant to meet a demand for miniaturization, because the wavelength of propagating electromagnetic wave is reduced to (1/xcex5 r)xc2xd in a dielectric;
2) A small dielectric loss in the high frequency region, i.e., a high Q value; and
3) A small change of resonant frequency to temperature, i.e., a small and stable temperature dependency of dielectric constant xcex5 r.
As such a dielectric ceramics, Japanese Patent Unexamined Publication No. 4-118807 (1992) discloses a dielectric ceramics composed of a CaO-TiO2-Nb2O5-XO system (wherein X is Zn, Mg, Co or Mn). However, this dielectric ceramics has the problem that a Q value by weight as 1 GHz is as low as about 1600 to 25000, and the temperature coefficient xcfx84 f of resonant frequency is as large as about 215 to 835 ppm/xc2x0 C. It has therefore been desired to increase Q value and decrease xcfx84 f.
Upon this, the present applicant has proposed an LnAlCaTi dielectric ceramics (wherein Ln is a rare earth element) in Japanese Patent Unexamined Publication No. 6-76633 (1994), an LnAISrCaTi dielectric ceramics (wherein Ln is a rare earth element) in Japanese Patent Unexamined Publication No. 11-278927 (1999), and an LnAlCaSrBaTi dielectric ceramics (wherein Ln is a rare earth element) in Japanese Patent Unexamined Publication No. 11-106255 (1999).
However, with the LnAlCaTi dielectric ceramics (Publication No. 6-76633), Q value is 20000 to 58000 when the dielectric constant xcex5 r is in the range of 30 to 47, and Q value is less than 35000 in some instances.
With the LnAlSrCaTi dielectric ceramics (Publication No. 11-278927), Q value is 20000 to 75000 when the dielectric constant xcex5 r is in the range of 30 to 48, and Q value is less than 35000 in some instances.
With the LnAlCaSrBaTi dielectric ceramics (Publication No. 11-106255), Q value is 30000 to 68000 when the dielectric constant xcex5 r is in the range of 31 to 47, and Q value is less than 35000 in some instances.
Hence there has been a desire for a dielectric ceramics having more improvements in Q value.
It is a major object of the present invention to provide a dielectric ceramics having a Q value of not less than 35000 when dielectric constant xcex5 r is in the range of 30 to 48, as well as a dielectric resonator.
It is another object of the present invention to provide a dielectric ceramics having a Q value of not less than 40000 when dielectric constant xcex5 r is not less than 40, as well as a dielectric resonator.
It is still another object of the present invention to provide a dielectric ceramics having a small and stable temperature dependency of dielectric constant xcex5 r, as well as a dielectric resonator.
A dielectric ceramics of the present invention in order to achieve the above objects is composed of an oxide containing, as a metal element, at least a rare earth element (Ln), Al, M (M is Ca and/or Sr) and Ti, at least part of the oxide of Al being present as a crystal phase of xcex2-Al2O3 and/or xcex8-Al2O3.
Of the crystals composed of the oxide containing a rare earth element (Ln), Al, M (M is Ca and/or Sr) and Ti, the crystal of which crystal system is hexagonal and/or orthorhombic is preferably present not less than 80% by volume.
A dielectric ceramics of the present invention preferably contains, as a metal element, at least one of Mn, W and Ta in an amount of 0.01 to 3% by weight as MnO2, WO3 and Ta2O5, respectively.
The crystal phase of xcex2-Al2O3 and/or xcex8-Al2O3 is preferably contained in a rate of {fraction (1/100000)} to 3% by volume.
A dielectric ceramics of the present invention contains, as a metal element, at least a rare earth element (Ln), Al, M (M is Ca and/or Sr) and Ti, and when its composition formula being expressed as follows:
aLn2O, bAl2O3 cMO dTiO2 (where 3xe2x89xa6xxe2x89xa64), 
a, b, c and d preferably satisfy the followings:
0.056xe2x89xa6axe2x89xa60.214
0.056xe2x89xa6bxe2x89xa60.214
0.286xe2x89xa6cxe2x89xa60.500
0.230xe2x89xa6dxe2x89xa60.470
a+b+c+d=1
The present invention also provides a dielectric ceramics containing, as a metal element, at least a rare earth element (Ln), Al, M (M is Ca and/or Sr) and Ti, characterized in that an average particle diameter D1 of the crystal of which main phase is a crystal phase composed of an oxide of M and Ti is larger than an average particle diameter D2 of the crystal of which main phase is a crystal phase composed of an oxide of a rare earth element (Ln) and Al.
Like the foregoing dielectric ceramics, this dielectric ceramics also has a large dielectric constant xcex5 r, a high Q value, and a small temperature dependency of dielectric constant xcex5 r.
The average particle diameter D1 of the crystal of which main phase is a crystal phase composed of an oxide of M and Ti is 12 xcexcmxe2x89xa6D1xe2x89xa6100 xcexcm, preferably 15 xcexcmxe2x89xa6D1xe2x89xa660 xcexcm, and the average particle diameter D2 of the crystal of which main phase is a crystal phase composed of an oxide of a rare earth element (Ln) and Al is 3 xcexcmxe2x89xa6D2xe2x89xa612 xcexcm, preferably 5 xcexcmxe2x89xa6D2xe2x89xa610 xcexcm. Further, it is preferable that this dielectric ceramics has the same composition formula as described above, and the mole ratios a, b, c and d have the same range as described above.
A dielectric resonator of the present invention is one in which the above-mentioned dielectric ceramics is disposed between a pair of input/output terminals so as to be operated by electromagnetic coupling.
These and other objects and advantages of the present invention will become more apparent from the following detailed description.